Sealing assemblies for turbomachines are generally located on both ends of a rotating shaft that is journalled with bearings. The sealing assemblies are used to prevent leakage into the atmosphere of process gas from a defined flow path through clearance openings formed between the rotating shaft and the turbomachine housing. Effectively sealing the process gas not only increases turbomachine efficiency, but in certain operations involving toxic or explosive gas under pressure, it also prevents dangerous gases from reaching the surrounding area and thereby causing volatile and possibly dangerous situations.
A typical sealing assembly may consist of a series of labyrinth seals and gas/oil seals axially spaced along the rotating shaft. Since each seal consumes a portion of axial shaft length, the centerline distance between the bearings is predictably increased, thus resulting in a longer and a heavier rotating shaft. Although all shafts deflect during rotation, an unnecessary increase in shaft length and weight can adversely affect shaft rotordynamics. For example, an increase in shaft length may lower the natural frequency of a shaft, thus resulting in higher potential amplitudes. Moreover, lower natural frequencies generally result in reduced critical speeds, and thus a less effective turbomachine.